Is that in Photoshop?
In InDesign it's best not to choose a font via the Character Styles panel; just (say) bold and Italic, so that if you change a font in Paragraph Styles it changes the fonts in Character Styles as well.
pay attention to the added video
We did, now it is time for you to pay attention to the [Brackets]: this font is missing, install it.
Note that this font is present in the system, but in the upper field you can see that it is written differently - a double space between the family name and the style. Moreover, when changing fonts from the drop-down list, this defect is saved in the name field. If this were a special case and constantly occurring , I would still agree with you. But this problem is random - in one new document it may occur with font # 1, in another new document it will not occur with font #1, in the third old document that has already been printed 30 times-it occurs with font #2 (just when changing the font from regular to italic). And this problem only appeared in indesign 2021
Roundtipping to IDML? Anyway, you can have multiple fonts with the same name but one being TrueType, another being OpenType etc. If the font was Gill Sans TT and you have Gill Sans OT, the font will be missing. Do you use any Fontmanager software/plug-in?
If you select text that uses a missing font, the Character panel or Control panel indicates that this font is missing by displaying it in brackets in the font style pop‑up menu.
the point is that the selected text does not contain any missing font or missing characters. The video shows that even when you select a font present in the system - character panel changes its name and makes it unavailable
can you share with us screenshot as in my immage bellow (type > find font)?
As you can see, the font family name duplicates the style. This is a new document, this error randomly occurs periodically when changing font
do you have the font only in package folder or installed and activated on your computer?